1. Field of the Invention
The present invention relates to a television tuner which supplies a power supply voltage to the respective circuits when a television signal is received, and cuts the supply of the power supply voltage to a specific circuit when the television signal is not received, thereby reducing the power consumption, and a video device using the television tuner.
2. Description of the Prior Art
A conventional television tuner (hereinafter referred to simply as a tuner) is provided with various circuits such as a high-frequency amplifier circuit, a mixer circuit, a local oscillation circuit and an intermediate-frequency amplifier circuit which are operated by supplying a power supply voltage, and a power supply terminal to which a power supply voltage is applied. A power supply voltage is applied from a television receiver with the tuner incorporated to the power supply terminal. The power supply voltage applied to the power supply terminal is supplied uniformly to these circuits.
In general, a television receiver is connected to a VCR and is used for reception of a television signal and for replay of the VCR. In either case, while the power supply of the television receiver is turned on, a power supply voltage is supplied to the tuner. Thus, the power supply voltage is supplied to the tuner not required to be operated when the VCR is replayed, resulting in a waste of power consumption.
Accordingly, an object of the present invention is to provide a tuner which stops supply of a power supply voltage to the inner circuits to save electric current consumed when a television signal is not received, and a video device using such a tuner.
To solve the foregoing problems, a television tuner of the present invention comprises at least a mixer circuit for frequency-converting a television signal to an intermediate-frequency signal, a local oscillation circuit for inputting a local oscillation signal to the mixer circuit, an intermediate-frequency amplifier circuit for amplifying the intermediate-frequency signal, and a PLL circuit for controlling the oscillating frequency of the local oscillation circuit, the television tuner further comprising switch means for supplying a power supply voltage to the mixer circuit, the local oscillation circuit, the intermediate-frequency amplifier circuit, and the PLL circuit, wherein when the television signal is received, the switch means is turned on, and when the television signal is not received, the switch means is turned off.
In the television tuner of the present invention, the mixer circuit, the local oscillation circuit, the intermediate-frequency amplifier circuit, and the PLL circuit are constructed in one package of an integrated circuit, the switch means is provided with a first switch element, the power supply voltage is supplied through the first switch element to the mixer circuit, the local oscillation circuit, the intermediate-frequency amplifier circuit, and the PLL circuit, and the first switch element is constructed in the integrated circuit.
In the television tuner of the present invention, a video intermediate-frequency circuit is provided outside the integrated circuit so as to process the intermediate-frequency signal amplified by the intermediate-frequency amplifier circuit, and to have a video signal output terminal for outputting a video signal and an audio signal output terminal for outputting an audio signal, the switch means is provided with a second switch element, the power supply voltage is supplied through the second switch element to the video intermediate-frequency circuit, and the second switch element is provided outside the integrated circuit.
A video device of the present invention comprises the television tuner as described above, an external video terminal to be fed an external video signal, an external audio terminal to be fed an external audio signal, a video signal process circuit, an audio signal process circuit, and video/audio switching means, wherein when the television signal is received, the video/audio switching means connects the video signal output terminal to the video signal process circuit and connects the audio signal output terminal to the audio signal process circuit, and when the television signal is not received, the video/audio switching means connects the external video terminal to the video signal process circuit and connects the external audio terminal to the audio signal process circuit.